Noun vs. adjective

Question

Why is Hay used for It is foggy? Isn't foggy an adjective?

Silvia Píriz · Accepted Answer

Hola David S.
Good question! In Spanish, hay is generally used with nouns, while está is used with adjectives.
For weather expressions, though, Spanish sometimes uses nouns where English uses adjectives.
For example:

Hay niebla = “It is foggy” (“niebla” = fog, a noun)

So even though foggy is an adjective in English, Spanish expresses the idea with the noun niebla, which is why hay is used.
By contrast:
Está nublado = “It is cloudy” (“nublado” is an adjective)
That’s why weather expressions can feel a bit inconsistent when translating directly from English.
Un saludo
Silvia